FIG. 1 is a network structure of the E-UMTS, a mobile communication system applicable to the related art and the present invention.
The E-UMTS system has been evolved from the UMTS system, for which the 3GPP is proceeding with the preparation of the basic specifications applicable thereto. The E-UMTS system can be classified as an LTE (Long Term Evolution) system.
With reference to FIG. 1, the E-UMTS network is divided into an E-UTRAN 20 and an EPC (Evolved Packet Core) 10. The E-UTRAN 20 includes a terminal (UE (User Equipment)), a base station (eNB or eNodeB) 21 and an AG (Access Gateway) 11 (which also can be expressed as ‘MME/UPE’). The AG 11 can be divided into a part for handling user traffic and a part for handling control traffic. The AG part for handling new user traffic and the AG part for handling control traffic can communicate with each other via newly defined interface.
One or more cells may exist in a single eNodeB (eNB) 21, and an interface for transmitting the user traffic and the control traffic can be used between the eNodeBs.
The EPC 10 may include an AG 11, a node for user registration of the UE, and the like. Also, in the UMTS of FIG. 1, an interface for discriminating the E-UTRAN 20 and the EPC 10 can be used. An S1 interface can connect a plurality of nodes (i.e., in a many-to-many manner) between the eNodeB 21 and the AG 11. The eNodeBs are connected with each other through an X2 interface, and the X2 interface is always present between adjacent eNodeBs in a meshed network structure.
Layers of a radio interface protocol between the UE and a network can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based upon the three lower layers of an open system interconnection (OSI) standard model that is well-known in the art of communication systems.
The first layer (L1) provides an information transfer service using a physical channel, and a radio resource control (RRC) layer positioned at the third layer (L3) serves to control radio resources between the terminal and the network, for which the RRC layer exchanges an RRC message between the terminal and the network. The RRC layer can be distributed so as to be positioned in network nodes such as the eNodeBs and the AGs, etc., or can be positioned only in the eNodeBs or in the AGs.
FIG. 2 illustrates a control plane structure of the radio access interface protocol between the terminal and the UTRAN based upon various 3GPP wireless access network standards.
The radio access interface protocol has horizontal layers including a physical layer, a data link layer and a network layer, and has vertical planes including a user plane for transmitting data information and a control plane for transmitting control signals.
The protocol layers can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based upon the three lower layers of an open system interconnection (OSI) standard model that is well-known in the art of communication systems. Each layer of the control plane of the radio protocol in FIG. 2 and the user plane of the radio protocol in FIG. 3 will now be described.
The physical layer, the first layer, provides an information transmission service to an upper layer by using a physical channel. The physical layer is connected with a medium access control (MAC) layer located at a higher level through a transport channel, and data between the MAC layer and the physical layer is transferred via the transport channel. Between different physical layers, namely, between physical layers of a transmission side and a reception side, data is transferred via the physical channel.
The MAC layer of Layer 2 provides services to a radio link control (RLC) layer (which is a higher layer) via a logical channel. The RLC layer of Layer 2 supports the transmission of data with reliability. It should be noted that the RLC layer in FIGS. 2 and 3 is depicted in dotted lines, because if the RLC functions are implemented in and performed by the MAC layer, the RLC layer itself may not need to exist. The PDCP layer of Layer 2 performs a header compression function that reduces unnecessary control information such that data being transmitted by employing Internet protocol (IP) packets, such as IPv4 or IPv6, can be efficiently sent over a radio (wireless) interface that has a relatively small bandwidth.
A radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane and controls logical channels, transport channels and the physical channels in relation to the configuration, reconfiguration, and release of the radio bearers (RBs). Here, the RB signifies a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN.
Downlink transport channels for transmitting data from the network to the terminal, include a broadcast channel (BCH) for transmitting system information and a downlink shared channel (SCH) for transmitting the user traffic or the control message. Downlink multicast, traffic of a broadcast service or a control message can be transmitted through the downlink SCH or through a separate downlink multicast channel (MCH).
Uplink transport channels for transmitting data from the terminal to the network include a random access channel (RACH) for transmitting an initial control message and an uplink SCH for transmitting the user traffic and the control message.